JP2019531508A - Processing of non-uniform diffraction grating - Google Patents

Abstract

A method of processing a non-uniform grid includes the steps of implanting ions of different densities into corresponding areas of a substrate, patterning a resist layer on the substrate, for example, by lithography, and a patterned resist layer And then removing the resist layer from the substrate and forming the substrate with at least one non-uniform grid having non-uniform characteristics associated with different densities of ions implanted in the area. Leaving a step. The method can further include processing a corresponding grating having a corresponding non-uniform property, for example by nanoimprint lithography, using the substrate having the grating as a mold.

Description

(Cross-reference of related applications)
This application claims the benefit of the filing date of US Provisional Application No. 62 / 404,555, filed Oct. 5, 2016. The entire contents of US Application No. 62 / 404,555 are incorporated herein by reference.

  The present disclosure relates generally to micro / nanostructure processing, and more particularly to processing of diffraction gratings.

  A diffraction grating is an optical component with a periodic structure that can split and diffract light into several beams traveling in different directions. The direction of these beams depends on the spacing of the grating, the wavelength of light, and the refractive indices of both the grating and the substrate. In some embodiments, the diffraction grating is composed of a set of slots with a spacing wider than the wavelength of the light, causing diffraction. After the light interacts with the grating, the diffracted light consists of the sum of the interference waves emanating from each slot in the grating. The depth of the slot affects the wave path length to each slot, and therefore the phase of the wave from each of the slots, and thus the diffraction efficiency of the slot. If the slots have a uniform depth, the slots in the grating can have a uniform diffraction efficiency. If the slots have a non-uniform depth, the slots in the grating can have non-uniform diffraction efficiency.

  Diffraction gratings have been processed using a variety of methods including photomasks, electron beam lithography, etching techniques, and holographic interference. However, diffraction gratings processed by the methods mentioned above are usually uniform gratings with uniform diffraction efficiency. There are only a few methods that have been developed to fabricate diffraction gratings with non-uniform diffraction efficiency, particularly with high resolution and large area.

  One aspect of the present disclosure features a method of processing a heterogeneous structure. The method includes implanting ions of different densities into a corresponding area of the substrate, patterning a resist layer on the substrate, and then etching the substrate using the patterned resist layer, Leaving the substrate with at least one non-uniform structure having non-uniform characteristics associated with different densities of ions implanted in the area.

  The method can include removing the resist layer from the substrate. The method may further include processing a corresponding non-uniform structure by nanoimprint lithography using a substrate having the non-uniform structure as a mold. Etching the substrate may include using reactive ion etching.

  The non-uniform structure can include a non-uniform grid. In some embodiments, the grid includes a binary grid with non-uniform depths corresponding to different densities of ions. In some embodiments, the grating includes a blazed grating with non-uniform depths corresponding to different densities of ions.

  In some implementations, implanting different densities of ions into corresponding areas of the substrate includes implanting first densities of ions into at least one target area along a first direction. And implanting ions of a second density into the target area along a second different direction, wherein the angle between the first direction and the second direction is greater than 0 degrees. And less than 180 degrees.

  In some implementations, implanting different densities of ions into corresponding areas of the substrate is moving a shutter between the ion source and the substrate along a direction, wherein the ions of different densities are An implanted area having a step along its direction. The shutter can be moved according to ion exposure profiles corresponding to different densities. In some embodiments, the shutter is a solid panel that is configured to block the passage of ions.

  In some embodiments, the shutter defines a plurality of through holes that allow ions to propagate from the ion source to the substrate. In some cases, the step of moving the shutter moves the shutter over the first target area in the substrate across the first spot at a first speed, and the ions move through the through-holes to the first. Allowing to pass over a target of the substrate and moving the shutter from the first spot to the second sequential spot at a second speed, the second sequential spot being a substrate The second velocity is faster than the first velocity, the second velocity is greater than the first velocity, and the first velocity moves the shutter across the second sequential spot so that the ions are Allowing to pass over the second target area through the through hole. In some cases, moving the shutter includes moving the shutter to a first spot above the first target area in the substrate, and stopping the shutter over a period of time at the first spot, a certain amount. Allowing the ions to pass through the through hole and over the first target area, and then moving the shutter to a second sequential spot over the second target area in the substrate. Including.

  In some implementations, the step of implanting different densities of ions into the corresponding area of the substrate is to place a shutter between the ion source and the substrate, the shutter being associated with a different ion permeability. A step comprising a plurality of parts. The plurality of portions may include a plurality of membranes with different thicknesses corresponding to different ion permeability.

  In some implementations, implanting different densities of ions into corresponding areas of the substrate locally implants different densities of ions into the corresponding areas of the substrate using a focused ion beam. Includes steps.

  The resist layer can include a photoresist, and the step of patterning the resist layer on the substrate includes depositing the photoresist layer on the substrate including the area, and using photolithography to emit the patterned light. Using the step of exposing the photoresist layer, etching one of the exposed and unexposed photoresist layers of the deposited photoresist layer, and developing the patterned resist layer on the substrate And a step of causing.

  The area without ion implantation may have a first etching sensitivity and the area with ion implantation may have a second etching sensitivity, between the first etching sensitivity and the second etching sensitivity. The ratio can exceed 2. The substrate can be a silicon substrate and the ions can include gallium ions. The heterogeneous structure can have an orientation resolution of 5,000 nm or less. The non-uniform structure can have an overall size of at least 1 mm.

  In some implementations, implanting different densities of ions into the corresponding area of the substrate includes implanting a first different density of ions into the first area of the substrate along the first direction. And implanting ions of a second different density into the second area of the substrate along the second direction, wherein the second area is equal to the first area in the substrate. Adjacent steps. The method further removes the resist layer from the substrate, the first grating in the first area, having a diffraction efficiency that increases along the first direction, and a second grating Leaving a substrate with a second grating in the area, the second grating having a diffraction efficiency increasing along the second direction. In some cases, the step of implanting ions of different densities into the corresponding area of the substrate comprises implanting a third different density of ions of the first area along a third direction different from the first direction. The angle between the first direction and the third direction is greater than 0 degrees and less than 180 degrees, and the third different density of ions is Less than a different density. In some cases, the step of implanting ions of different densities into the corresponding area of the substrate comprises transferring ions of a fourth different density in the second area along a fourth direction different from the second direction. The angle between the second direction and the fourth direction is greater than 0 degrees and less than 180 degrees, and the fourth different density of ions is a second ion density Less than a different density.

  Another aspect of the present disclosure is a diffractive optical element (DOE) having one or more layers on a substrate, each layer comprising an orthogonal pupil expansion (OPE) diffractive element and an exit pupil expansion (EPE) diffractive element. A first diffractive optical element (DOE), wherein the OPE diffractive element is configured to deflect a portion of the input light beam propagating in the substrate into the EPE diffractive element in the substrate. The EPE diffractive element comprises a second non-uniform grating configured to deflect a portion of the deflected light beam from the OPE diffractive element out of the substrate. To do. The device may include an internal coupling element (ICO) integrated into the substrate, configured to receive an input light beam from outside the substrate and transmit the input light beam to a DOE in the substrate.

  The first non-uniform grating may have a first characteristic that varies along a first direction, and the second non-uniform grating varies along a second direction relative to the first direction. The first non-uniform grating may have a second characteristic, the first non-uniform grating may have an increasing diffraction efficiency along the first direction, and the second non-uniform grating may be along the second direction, Can have increased diffraction efficiency. In some embodiments, the angle between the first direction and the second direction is between 45 degrees and 90 degrees.

  In some implementations, the first non-uniform grating has a third characteristic that varies along a third direction that is different from the first direction, between the first direction and the third direction. The angle of is greater than 0 degrees and less than 180 degrees. In some implementations, the second non-uniform grating has a fourth characteristic that varies along a fourth direction that is different from the second direction, between the second direction and the fourth direction. The angle of is greater than 0 degrees and less than 180 degrees.

  The details of one or more disclosed implementations are set forth in the accompanying drawings and the description below. Other features, aspects, and advantages will be apparent from the description, drawings, and claims.

FIG. 1 is a flow diagram of an exemplary process for processing a non-uniform diffraction grating in a substrate. FIG. 2 shows an exemplary cross-sectional view of the substrate after different steps of the processing process of FIG. FIG. 3A is a schematic diagram of a first exemplary method of implanting various densities of ions into a substrate using a movable shutter with a solid panel. FIG. 3B is a schematic diagram of a second exemplary method of implanting various densities of ions into a substrate using a movable shutter with through holes. FIG. 3C is a schematic diagram of a third exemplary method of implanting various densities of ions into a substrate using a shutter having portions with various transmittances. FIG. 3D is a schematic diagram of a fourth exemplary method of implanting various densities of ions into a substrate using a focused ion beam (FIB). FIG. 4A shows the experimental results of small area non-uniform ion implantation and etching into a silicon substrate. FIG. 4B shows the experimental results of large area non-uniform ion implantation and etching into a silicon substrate. FIG. 5 shows the experimental results of a non-uniform diffraction grating fabricated using ion implantation and lithography, according to an exemplary embodiment. FIG. 6 shows an exemplary optical system that uses a non-uniform diffraction grating.

  The present disclosure relates to methods, apparatus, and systems for processing micro / nanostructures, particularly non-uniform micro / nano structures, eg, diffraction gratings, and non-uniform micro / nano, eg, in optical systems. The use of the structure will be described. The technique employs implantation of spatially different densities of ions into corresponding areas of the substrate. The ion implantation can change the etching sensitivity of the substrate such that the etching sensitivity of the ion implantation area and the non-implanted (ie, undoped) area are different. Then, by combining with a patterning technique, such as lithography or nanoimprint, for selectively patterning a protective resist layer on the substrate, the technique allows the substrate to be etched at different depths within the ion implanted and non-implanted areas. / Height so that non-uniform micro / nanostructures can be obtained. As a result, a gradient or modulation in ion density or concentration in the substrate results in a structure (eg, a grating) with a modulated height / depth profile. Any lithographic technique (including any type of photolithography or electron beam lithography) or any type of resist patterning technique may be used herein. Furthermore, substrates with non-uniform structures can be used as molds for mass production of corresponding non-uniform structures with variable height / depth patterns, for example in nanoimprint lithography. Ion implantation can be controlled spatially, for example, in one, two, or three dimensions. Also, combining spatially controlled ion implantation with resist patterning (eg, lithography) and etching, the technology is more flexible in micro / nanostructure design and processing than standard lithography or ion implantation techniques. Allow sex. The technology is applied, for example, to a substrate with a large area over 1 mm in size and / or at a high speed, for example with a large depth range of 5 nm to 1,000 nm, for example as high as about 5-10 nm Depth resolution can be achieved.

  The technology can be applied to any suitable micro / nanostructure, such as a lattice, using any suitable material, such as silicon, glass, or polymer, and any suitable ionic species, such as gallium ions or argon. Can be applied to processing. For illustrative purposes only, the following description is primarily directed to processing non-uniform diffraction gratings on silicon substrates using gallium ion implantation.

  FIG. 1 is a flow diagram of an exemplary process 100 for processing a non-uniform diffraction grating in a substrate, and FIG. 2 shows an exemplary cross-sectional view 200 of the substrate after different processing steps of the processing process 100.

  The substrate can optionally be prepared for ion implantation (101). The substrate can be pretreated, for example, by cleaning the surface of the substrate. In some cases, wet chemical processing, such as solution-based RCA cleaning procedures, can be used to remove any organic or inorganic contaminants present on the substrate. The solution can contain hydrogen peroxide, trichlorethylene, acetone, or methanol.

  The substrate is implanted with ions of various densities (102). As described above, the substrate can be a silicon substrate, eg, a silicon wafer. The size of the silicon wafer can be 2 inches, 4 inches, 6 inches, or any other desired size. The ions can be gallium ions.

  As discussed in further detail in FIGS. 3A-3D, ion implantation can be spatially controlled to locally modulate the ion density within the substrate. Any suitable profile of ion density within the substrate can be achieved, for example, linear or sinusoidal. The profile can be one-dimensional (eg, for a linear lattice), two-dimensional (eg, for a circular lattice or any two-dimensional nanostructure), or three-dimensional (eg, for a nanostructure with a pyramid shape). (I) in FIG. 2 shows a substrate 202 with a linear profile of ion density 204 after ion implantation, where the ions 204 implanted into the substrate 202 are in a direction of the substrate 202 from the surface of the substrate 202, For example, it has a density (or depth) that increases linearly along the longitudinal direction. The ion implantation profile can be predetermined based on the desired ion density profile in the substrate. Based on the predetermined ion implantation profile, the shutter varies the exposure time of different areas of the substrate to the ion source, at a rate to achieve the desired ion density profile in the substrate, for example, It can be moved in one, two, or three dimensions.

  Implanted ions can change the etch sensitivity of the substrate, which can cause etch delay behavior in etching (ie, masking effects) due to several mechanisms. The first is a physical modification of the implanted area by impurity atoms, which changes the lattice constant, causes the associated strain effect, and ultimately slows the etch. The second is a chemical reaction with different ion implantation areas and non-implantation areas with the etch chemistry. Thus, the etching chemistry can also affect the etching sensitivity of the ion implanted substrate. In certain embodiments, the ratio of etch sensitivity (i.e., etch rate ratio) of unimplanted silicon and gallium ion implanted silicon is greater than 1: 1, such as 2: 1, 3: 1, 5: 1, 10 :. 1, 100: 1, or 1,000: 1.

In some cases, there may be a maximum exposure dose for ion implantation, below which the final structure height or depth exhibits a substantially linear dependence on the ion implantation exposure. Beyond the maximum exposure, ion sputtering becomes very extensive and can over-emphasize the masking effect. That is, the etch rate ratio can decrease with further increases in ion content. In a particular example, the maximum exposure of gallium ions for silicon is about 1.5 × 10 ¹⁶ per cm ² .

  A resist layer is patterned on the substrate (104). The resist layer can be patterned by any suitable patterning technique, including lithography or nanoimprint. In some implementations, the resist layer is a photoresist layer and the lithography used is photolithography. The resist layer can be a positive photoresist layer or a negative photoresist layer. The resist layer can be a protective resist layer for protecting the substrate under the resist layer from etching.

  In some embodiments, patterning the resist layer on the substrate comprises depositing a photoresist layer on the substrate including the ion implantation area and using patterned light using photolithography. Exposing the photoresist layer and exposing the exposed photoresist layer (eg, with respect to a positive photoresist layer) or an unexposed photoresist (eg, with respect to a negative photoresist layer) Etching the layer and developing the patterned resist layer on the substrate. FIG. 2 (II) shows a substrate with a patterned protective resist layer 206.

  By resist patterning and etching, the pattern profile of the patterned resist layer can be transferred into the substrate. In some embodiments, the profile of the patterned protective resist layer can be pre-determined or pre-designed based on the desired lattice profile and various ion density profiles within the substrate. The azimuthal resolution of the grating can be determined by the resolution of the patterned protective resist layer, and thus the resolution of the lithographic technique. The grating may have an azimuth resolution of 5,000 nm or less, in particular less than 1,000 nm, 500 nm, 200 nm, or 100 nm.

The substrate with the patterned resist layer is etched (106). As noted above, ion implantation changes the etch sensitivity of the substrate, and etch chemistry can also affect the etch sensitivity of the substrate. The substrate can be etched by dry etching, wet etching, or any suitable etching method. In some embodiments, the substrate is etched by reactive ion etching (RIE), eg, room temperature RIE or cryogenic RIE. For example, a silicon substrate with gallium ion implantation is etched without oxygen by RIE containing oxygen (eg, SF ₆ / O ₂ plasma) or through RIE with fluorine-based chemicals (eg, CF ₄ ). Can.

  The etch sensitivity of the substrate varies with different (or different) densities of ions implanted into the corresponding area of the substrate. Using the same etch time, areas with different (or different) densities of ions can be etched and have different (or different) depths corresponding to different (or different) densities of ions. For example, an area with a higher density of ions has a smaller etch depth than an area with a lower density of ions. The non-implanted area has the highest etch depth. FIG. 2 (III) shows a substrate with an etching depth 208 that decreases from left to right, corresponding to increasing density of ions implanted into the substrate. Substrates with various etch depths have patterns corresponding to the patterned protective resist layer on the substrate.

  In some cases, an etch depth resolution of about 5-10 nm can be achieved. The etching depth can be within a wide range of, for example, 5 nm to 200 nm. Lateral diffusion of ions during ion implantation can limit the feature size of the fabricated grating, eg, the azimuthal resolution of the grating period. Lateral diffusion depends on the acceleration voltage. In some embodiments, the diffusion radius is 12 nm for an acceleration voltage of 30 KeV and 45 nm for an acceleration voltage of 100 KeV.

  The resist layer is removed from the substrate to obtain at least one non-uniform grid (108). The protective resist layer can be removed from the substrate after it is no longer needed. In some cases, the resist layer is removed by a liquid resist stripper that chemically modifies the resist so that the resist no longer adheres to the substrate. In some cases, the resist layer is removed by a plasma containing oxygen.

  A non-uniform lattice may have profiles associated with various densities of ions in the area. As an example, FIG. 2 (IV) shows a diffraction grating having a linearly varying depth 208 along the direction of the grating. The depth corresponds to different densities of ions along that direction, and the grating can have different diffraction efficiencies along that direction. In some embodiments, the non-uniform grid is a binary grid with non-uniform depths corresponding to various densities of ions, as illustrated by (IV) in FIG.

  In some embodiments, the non-uniform grating is a blazed grating with non-uniform depths corresponding to various densities of ions. For example, a serrated profile in ion exposure can result in a blazed profile after etching. The structure can be patterned with the following concepts. That is, the upper blaze portion receives the maximum amount, and modulation of the blaze angle is performed by varying the slope of the amount gradient within each period.

  Optionally, the substrate having a non-uniform grating is used as a mold for processing the corresponding grating by nanoimprint lithography, including, for example, thermoplastic nanoimprint lithography, photo nanoimprint lithography, or resist-free direct thermal nanoimprint lithography. (110). This step can mass produce the corresponding grid on a new substrate. The new substrate can include silicon, glass, or polymer.

  The above description is an exemplary process for processing a non-uniform diffraction grating. The process achieves different etching sensitivities in the substrate and thus uses different densities of ion implantation to obtain a non-uniform diffraction grating. The disclosed process can be adapted to process any heterogeneous micro / nanostructure in a substrate. For example, in some implementations, in step 106 of FIG. 1, the substrate is etched to have at least one non-uniform structure having non-uniform characteristics associated with different densities of ions implanted in the area. The The remaining resist layer can be kept on the substrate, for example, as a protective layer for the formed heterogeneous structure in the substrate or other functional layer. In some embodiments, the resist layer is deposited substantially uniformly on the substrate by chemical vapor deposition (CVD), eg, metal organic chemical vapor deposition (MOCVD). In some embodiments, additional layers may be further deposited on the substrate and resist layer.

  3A-3D illustrate different exemplary methods for implanting various densities of ions into a substrate that may be performed in step 102 of process 100 of FIG.

  Referring to FIG. 3A, the first exemplary method 300 uses a movable shutter with a solid panel 304 to move between the ion source 302 and the substrate 306 to change the exposure for different portions of the substrate 306. Let Shutter 304 is configured to completely block the passage of ions. For example, the shutter 304 can be made from a solid panel, such as steel. The shutter 304 is controlled or powered to move.

  Figures (I), (II), and (III) of FIG. 3A schematically illustrate the ion source 302, movable shutter 304, and substrate 306 at different time zones. FIG. 3A (I) shows that prior to ion implantation, a movable shutter 304 is positioned between the ion source 302 and the substrate 306 to completely prevent ions from propagating from the ion source 302 to the substrate 306. Indicates. Next, as illustrated in FIG. 3A (II), when the movable shutter 304 is moved along the direction from right to left, for example, the substrate 306 starts to receive ion irradiation from the ion source 302. . The right portion of the substrate 306 experiences a longer exposure than the left portion of the substrate, and thus the right portion of the substrate has a higher density of ions implanted into the substrate. The substrate 306 thus has various densities of ions along its direction. The shutter 304 can be moved based on a profile, eg, a predetermined profile based on a desired ion density profile in the substrate. FIG. 3a (III) shows that when the movable shutter 304 is moved out of the space between the ion source 302 and the substrate 306, the substrate 306 has different densities of ions along its direction, eg, It shows having an ion density that increases from left to right with increasing ion exposure. In some cases, the substrate 306 is further exposed to the ion source 302 without moving the shutter 304 therebetween until the desired ion density profile is achieved across the substrate.

  FIG. 3B is a schematic diagram of a second exemplary method 350 for implanting various densities of ions into a substrate using a movable shutter 352 with a through hole 354. Through-hole 354 allows ions from an ion source (not shown here) to pass through and strike the substrate 356. Other parts of the movable shutter 352 can be made from a solid material, such as steel, to prevent ions from passing through. The nature, such as width and / or period, of the through-hole 354 in the movable shutter 352 can be determined based on the desired profile of the structure, eg, the grating.

  Figures (I), (II), and (III) of FIG. 3B schematically show the movable shutter 352 and the substrate 356 in different time zones. This indicates that as the movable shutter 352 moves along the direction from right to left, the area exposed in higher amounts has a higher ion density. In some implementations, the shutter 352 constantly moves along that direction. As the shutter 352 moves across the first spot corresponding to the first target area to be ion implanted, the shutter 352 may allow a certain amount of ions to pass through the through-hole 354 to the first target area. So that it can move at a slower speed. As the shutter moves from the first spot to a second sequential spot corresponding to the second target area to be ion implanted, the shutter can move at a faster speed, for example, the speed is two When moving between spots, it can be fast enough to ignore ion exposure on the substrate. As the shutter moves across the second spot, the shutter speed is adjusted from a faster speed to a slower speed. In some implementations, the shutter 352 moves discretely along that direction. When the shutter 352 moves to the first spot, the shutter 352 stops and allows a certain amount of ions to pass through the through-hole 354 to the first target area. The shutter 352 then moves to the second spot and stops for ion implantation on the second target area. In some cases, the ion source is blocked when the shutter 352 moves between the two spots. In some cases, the shutter 352 moves at high speed between the two spots and the ion source remains on.

  Compared to the substrate 306 of FIG. 3A having various densities of ions across the substrate 306, the substrate 356 has a patterned ion implantation profile across the substrate 356. That is, ions are periodically implanted into the substrate with various densities along that direction. In some cases, the substrate 356 with various patterned ion implantations is etched directly without using additional patterning techniques to obtain a grating with various depths / heights. Can be. In some cases, the substrate 356 can also be etched by combining with a patterning technique, eg, a lithographic technique, to create any desired etching pattern. In some implementations, the length of movable shutter 352 is less than the length of substrate 356, as illustrated in FIG. 3B. In some implementations, the length of movable shutter 352 is greater than or the same as the length of substrate 356. The movable shutter 352 is positioned to completely cover the substrate 356 in the initial position and then moved discretely, allowing different portions of the substrate 356 to have different exposure times for ion implantation. be able to.

  FIG. 3C is a schematic diagram of a third exemplary method 370 for implanting various densities of ions into the substrate 376 using a shutter 372 having portions 374 with various transmittances. Note that shutter 372 can be statically positioned (or moved) between an ion source (not shown here) and substrate 376. Portion 374 may have various transmittances within shutter 372 that may allow different proportions of ions to propagate. In some implementations, the portion 374 is made from a film, eg, a silicon film, with different thicknesses that correspond to different ion permeability.

  In certain embodiments, the shutter 372 has five portions with a series of transmissivities that vary, for example, from 10% to 30%, 50%, 70%, 90% in FIG. 3C (from left to right). Configured as follows. The remaining part of the shutter 372 has a transmission of 0%, i.e. completely blocks the passage of ions. In such a manner, using the same exposure time, different areas of the substrate may experience different ion exposures and thus have different densities of ions. As a result, the substrate 376 may also have patterned ion implantation with varying densities across the substrate, similar to FIG. 3B. The substrate 376 can also be etched with or without lithographic techniques.

  The method illustrated in FIGS. 3A-3C can be implemented by a standard ion implantation system with different types of shutters, which allows, for example, a large implantation area at a high speed, such as a size greater than 1 mm. Can do.

  FIG. 3D is a schematic diagram of a fourth exemplary method 390 for implanting various densities of ions into a substrate using a focused ion beam (FIB). Curve 392 shows the FIB exposure profile that can be determined by the profile of the desired ion density in the substrate 396. The FIB method makes it possible to achieve high resolution, but it can be difficult to pattern large areas, for example, with a size greater than 1 mm.

The above description shows exemplary methods for implanting various densities of ions into a substrate. Other methods can also be used to accomplish this. For illustrative purposes only, FIGS. 3A-3D show various densities of ions implanted into the substrate along one dimension. It should be noted that the method can be applied to achieve different densities of ions implanted in two dimensions with any desired profile, for example linear, sinusoidal, or circular. .
(Exemplary experimental results)

FIG. 4A shows the experimental results of a small area non-uniform diffraction grating fabricated using gallium ion implantation in a silicon substrate. The focused ion beam (FIB) is initially linearly varying from 10 ¹⁵ (10 ¹⁵ to 10 ¹⁶ / cm ² ) into 10 lines (with a width of 100 nm and a length of 50 μm). Different amounts are used to locally implant gallium ions into the silicon substrate. The substrate is then etched based on the SF ₆ / O ₂ cryogenic process. FIG. 410 shows a scanning electron microscope (SEM) image of the processed lattice, and FIG. 420 shows a corresponding atomic force microscope (AFM) image of the processed lattice. The grating has a height variation ranging from 60 to 90 nm.

  Compared to FIG. 4A, FIG. 4B shows the experimental results of a large area non-uniform diffraction grating fabricated using gallium ion implantation in a silicon substrate using the same FIB and etching method. FIG. 430 shows an AFM image of the processed grating in which different amounts of ions are implanted in a 10 micron wide band, while FIG. 440 shows the corresponding height profile of the processed grating.

  FIG. 5 shows the experimental results of a non-uniform diffraction grating fabricated using ion implantation, according to an exemplary embodiment. Compared to FIGS. 4A and 4B, the diffraction grating is fabricated by combining FIB ion implantation, optical lithography patterning, and etching together.

Initially, the substrate 510 is modified by FIB to implant various densities of ions into different portions of the area 510 of the substrate 510. The substrate 510 is then patterned by photolithography using a protective photoresist layer. FIG. 5A shows a SEM image of the substrate after patterning, including photoresist line 512 and ion implantation area. Photoresist line 512 has a width of 5 microns. Finally, the substrate 510 is etched and the protective photoresist layer is removed. FIG. 5B shows an AFM image 520 of the processed grid with different depths, while FIG. 5C shows the corresponding height profile 530 of the processed grid. Experimental results show the feasibility of combining ion implantation with lithography and etching techniques to create diffraction gratings with various depths.
(Example system)

  FIG. 6 shows an exemplary optical system 600 that uses a non-uniform diffraction grating. The optical system 600 can be used for virtual reality and augmented reality applications. In some implementations, the optical system 600 has an eyepiece that includes an internally coupled optical (ICO) element 602 and a diffractive optical element (DOE) 604. The eyepieces are incorporated herein by reference in their entirety, “Methods and systems for generating content display with a virtual or augmented reality” Can be implemented as described in published US patent application Ser. No. 14 / 726,424.

  The ICO 602 and the DOE 604 can be mounted in the substrate 610. The substrate 610 can be transparent, eg, glass. The DOE 604 may have one or more layers, each layer including an orthogonal pupil expansion (OPE) diffractive element 606 and an exit pupil expansion (EPE) diffractive element 608.

  The ICO element 602 is configured to receive an input light beam from a projector, for example, and transmit the input light beam to the DOE 604 in the substrate 610. For example, the substrate 610 includes a waveguide (not shown here), and the ICO element 602 transmits the input light beam into the waveguide coupled to the DOE 604. The input light beam travels into the waveguide by total internal reflection (TIR). The OPE diffractive element 606 on a layer is configured to deflect a portion of the input light beam and, in turn, a portion of the deflected light beam out of the substrate 610, eg, toward the user's eye. Configured to deflect the EPE diffractive element 608.

  The OPE diffractive element 606 and the EPE diffractive element 608 can be arranged side-by-side in the same plane or on the same layer. In order to emit a light beam out of the substrate, the DOE 604 is configured to diffract the light beam across the DOE 604 using, for example, a selective distribution of diffraction. In some embodiments, the distribution of diffracted light is substantially uniform. In some embodiments, the amount of light diffracted is variable across the DOE 604 profile, for example, in an increasing gradient or in a randomized fashion. For example, as the light beam propagates through the DOE 604 and is gradually deflected by the OPE diffractive element 606 and the EPE diffractive element 608, the intensity of the light beam decreases, so that the diffraction efficiency of the DOE 604 is along the propagation path of the light beam. Can be configured to gradually increase.

  In some implementations, the OPE diffractive element 606 includes a first non-uniform grating positioned along a first direction from bottom to top, for example, as shown in FIG. The EPE diffractive element 608 includes a second non-uniform grating positioned along a second direction from left to right, for example, as shown in FIG. The angle between the first direction and the second direction can be in the range of 0-90 degrees. In some cases, the angle is between 45 degrees and 90 degrees. In some cases, the angle is between 80 degrees and 90 degrees. In certain embodiments, the second direction is perpendicular to the first direction. The first non-uniform grating can be a diffraction grating with a linearly varying depth along the first direction, and therefore the first non-uniform grating is a diffraction that gradually increases along the first direction. May have efficiency. The second non-uniform grating can be a diffraction grating with a linearly varying depth along the second direction, and thus the second non-uniform grating is a diffraction that gradually increases along the second direction. May have efficiency.

  In some implementations, the OPE diffractive element 606 and the EPE diffractive element 608 include a linear diffractive structure, a circular diffractive structure, a radially symmetric diffractive structure, or any combination thereof. The OPE diffractive element 606 and the EPE diffractive element 608 include both linear grating structures and circularly or radially symmetric diffractive elements, and can both deflect and focus the light beam.

  The first and second non-uniform gratings can be processed by a process similar to process 300 of FIG. The process implants a first variety of densities of ions along a first direction into a first area of a substrate, eg, substrate 610, and a second variety of ions along a second direction. Starting with the step of implanting ions of the density into the second area of the substrate, the second area being adjacent to the first area in the substrate. The shutter, eg, shutter 204 in FIG. 2A, can be moved in two dimensions to implement ion implantation into the first and second areas. A protective resist layer is then deposited on the substrate and patterned, for example, by photolithography. The process continues with etching the substrate having the patterned protective resist layer and developing various depths within the first area and the second area. Finally, the patterned protective resist layer is removed to obtain a substrate having a first non-uniform grid within a first area and a second non-uniform grid within a second area. . The first non-uniform grating has a non-uniform depth along the first direction and thus a non-uniform diffraction efficiency along the first direction. The second non-uniform grating has a non-uniform depth along the second direction and thus a non-uniform diffraction efficiency along the second direction. In some implementations, a substrate having first and second non-uniform gratings is used as a mask for mass production of corresponding non-uniform gratings in other substrates by nanoimprint lithography.

  In some implementations, the DOE 604 has at least one along its diffractive structure, eg, along the first non-uniform grating of the OPE diffractive element 606 and / or the second non-uniform grating of the EPE diffractive element 608. Includes dithering features. For example, the dithering feature along the first non-uniform grid may be characterized by additional ion implantation along a third direction along which the first area in the substrate is different from the first direction in which the ions are implanted. Can be achieved. Additional ion implantation may be less than previous ion implantation on the first area. The angle between these first and third directions may be greater than 0 degrees and less than 180 degrees, for example 90 degrees. The dithering feature along the second non-uniform grating performs additional ion implantation along the fourth direction along which the second area in the substrate is different from the second direction in which the ions are implanted. Can be achieved. The additional ion implantation may be less than the previous ion implantation on the second area. The angle between these second and fourth directions may be greater than 0 degrees and less than 180 degrees, for example 90 degrees.

  The above description is an exemplary system that includes a non-uniform diffraction grating. The system employs a diffraction grating with non-uniform diffraction efficiency along the light propagation path so that a uniform diffracted light can be achieved when the light propagates and is gradually deflected along the path To do. The disclosed implementation can be employed in any system that requires various diffraction efficiencies.

  Several implementations have been described. However, it should be understood that various modifications can be made without departing from the spirit and scope of the techniques and devices described herein. The features shown in each of the implementations can be used independently or in combination with each other. Additional features and variations may be included within this implementation as well. Thus, other implementations are within the scope of the following claims.

Claims (32)

A method of processing a heterogeneous structure, the method comprising:
Implanting ions of different densities into the corresponding area of the substrate;
Patterning a resist layer on the substrate;
The substrate is then etched using the patterned resist layer and the substrate with at least one non-uniform structure having non-uniform characteristics associated with the different density of ions implanted in the area. A method including leaving.   The method of claim 1, further comprising removing the resist layer from the substrate.   The method of claim 2, further comprising processing the corresponding non-uniform structure by nanoimprint lithography using the substrate having the non-uniform structure as a mold.   The method of claim 2, wherein the non-uniform structure comprises a non-uniform grid.   The method of claim 4, wherein the grating comprises a binary grating with a non-uniform depth corresponding to the different density of ions.   The method of claim 4, wherein the grating comprises a blazed grating with a non-uniform depth corresponding to the different density of ions. Implanting different densities of ions into the corresponding area of the substrate
Implanting a first density of ions into the at least one target area along a first direction;
Implanting a second density of ions into the target area along a second different direction, wherein the angle between the first direction and the second direction is greater than 0 degrees. The method of claim 1, comprising: less than 180 degrees. Implanting ions of different densities into the corresponding areas of the substrate,
Moving the shutter between an ion source and the substrate along a direction, wherein the implanted area with the different density of ions is along the direction. The method described in 1.   The method of claim 8, wherein the shutter is moved according to an ion exposure profile corresponding to the different densities.   The method of claim 8, wherein the shutter is a solid panel configured to block the passage of ions.   The method of claim 8, wherein the shutter defines a plurality of through holes that allow ions to propagate from the ion source to the substrate. Moving the shutter includes
At a first velocity, traverse a first spot and move the shutter over a first target area in the substrate and ions pass through the through hole and onto the first target area. Make it possible, and
Moving the shutter from the first spot to a second sequential spot at a second speed, wherein the second sequential spot is above a second target area in the substrate; The second speed is faster than the first speed;
Moving the shutter across the second sequential spot at the first speed to allow ions to pass over the second target area through the through-hole. The method of claim 11. Moving the shutter includes
Moving the shutter to a first spot above a first target area in the substrate;
Stopping the shutter for a period of time in the first spot, allowing an amount of ions to pass through the through-hole and over the first target area;
And moving the shutter to a second sequential spot over a second target area in the substrate. Implanting ions of different densities into the corresponding areas of the substrate,
The method of claim 1, comprising installing a shutter between an ion source and the substrate, the shutter comprising a plurality of portions with different ion transmission rates.   15. The method of claim 14, wherein the plurality of portions comprises a plurality of membranes with different thicknesses corresponding to the different ion permeability. Implanting ions of different densities into the corresponding areas of the substrate,
The method of claim 1, comprising using a focused ion beam to locally implant the different densities of ions into a corresponding area of the substrate. The resist layer comprises a photoresist, and patterning the resist layer on the substrate
Depositing a photoresist layer on the substrate including the area;
Using photolithography to expose the photoresist layer with patterned light;
Etching one of the exposed and unexposed photoresist layers of the deposited photoresist layer and developing the patterned resist layer on the substrate. Item 2. The method according to Item 1.   The method of claim 1, wherein etching the substrate comprises using reactive ion etching.   The area without ion implantation has a first etching sensitivity, the area with ion implantation has a second etching sensitivity, and is between the first etching sensitivity and the second etching sensitivity. The method of claim 1, wherein the ratio is greater than two.   The method of claim 1, wherein the substrate is a silicon substrate and the ions comprise gallium ions.   The method of claim 1, wherein the heterogeneous structure has an orientation resolution of 5,000 nm or less.   The method of claim 1, wherein the heterogeneous structure has an overall size of at least 1 mm. Implanting ions of different densities into the corresponding areas of the substrate,
Implanting a first different density of ions into the first area of the substrate along a first direction;
Implanting ions of a second different density into a second area of the substrate along a second direction, wherein the second area is equal to the first area in the substrate. The method of claim 1, comprising: adjoining. Removing the resist layer from the substrate;
A first grating in the first area, wherein the first grating has a diffraction efficiency that increases along the first direction;
A second grating within the second area, wherein the second grating leaves the substrate with a second grating having a diffraction efficiency that increases along the second direction. 24. The method of claim 23, further comprising: Implanting ions of different densities into the corresponding areas of the substrate,
Implanting ions of a third different density into the first area along a third direction different from the first direction, wherein the first direction and the third direction; 24. The method of claim 23, wherein the angle between is greater than 0 degrees and less than 180 degrees, and the third different density of the ions is less than the first different density of the ions. . Implanting ions of different densities into the corresponding areas of the substrate,
Implanting ions of a fourth different density into the second area along a fourth direction different from the second direction, wherein the second direction and the fourth direction; 24. The method of claim 23, wherein the angle between is greater than 0 degrees and less than 180 degrees, and the fourth different density of the ions is less than the second different density of the ions. . A device,
A diffractive optical element (DOE) having one or more layers on a substrate, each layer comprising an orthogonal pupil expansion (OPE) diffractive element and an exit pupil expansion (EPE) diffractive element. )
With
The OPE diffractive element comprises a first non-uniform grating configured to deflect a portion of an input light beam propagating in the substrate into the EPE diffractive element in the substrate;
The device, wherein the EPE diffractive element comprises a second non-uniform grating configured to deflect a portion of the deflected light beam from the OPE diffractive element out of the substrate. The first non-uniform grating has a first characteristic that varies along a first direction, and the second non-uniform grating varies along a second direction relative to the first direction. Having a second characteristic;
The first non-uniform grating has a diffraction efficiency that increases along the first direction, and the second non-uniform grating has a diffraction efficiency that increases along the second direction. Item 28. The device according to Item 27.   30. The device of claim 28, wherein an angle between the first direction and the second direction is between 45 degrees and 90 degrees.   The first non-uniform lattice has a third characteristic that varies along a third direction different from the first direction, and an angle between the first direction and the third direction is 30. The device of claim 28, wherein the device is greater than 0 degrees and less than 180 degrees.   The second non-uniform grating has a fourth characteristic that varies along a fourth direction different from the second direction, and an angle between the second direction and the fourth direction is 30. The device of claim 28, wherein the device is greater than 0 degrees and less than 180 degrees.   And further comprising an internal coupling element (ICO) integrated within the substrate, configured to receive the input light beam from outside the substrate and transmit the input light beam to a DOE in the substrate. Item 28. The device according to Item 27.